This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The goal of the experiment is to determine the mechanism of lactose/H+ symport by the lactose permease of E. coli (LacY), a paradigm for the Major Facilitator Superfamily (MFS) of membrane transport proteins. We plan to solve structures of different conformations of LacY and improve the resolution and quality of currently available crystal structure. For this we obtained crystals of different LacY substrates complexes, mutants, or homologues. We need to screen several hundred crystals and then perform MAD experiments on selected crystals. This requires regular access to synchrotron radiation